uploading transparent .png to wordpress

Hey guys. I'm wanting to upload some transparent .pngs into the media library. I've got a sweet ajax theme that floats the text & images over a transparency w/a background image. Having images that could be transparent and just sit on top of things would be super-amazing..

how is do?

example:

http://peterfae.intothemythica.com/2014/07/24/heroes-and-heroines/

(just a quickie, but you get the idea)